Scalable bilayer thin coatings with enhanced thermal dissipation for passive daytime radiative cooling

Passive daytime radiative cooling (PDRC) is a ground-breaking strategy to realize subambient cooling without any extra energy and environmental pollution. However, the challenge is how to work out the contradiction between thick films (typically 300–800 μm) for efficient cooling and thin films for practicality. Herein, we propose a scalable bilayer thin PDRC coating consisting of waterborne polyurethane / hollow glass beads top layer and poly(vinylidene fluoride-co-hexafluoropropene) / zinc oxide nanocubes underlayer, exhibiting sufficient solar reflectance (0.92), longwave infrared emissivity (0.93) and a relatively high thermal conductivity (1.702 W m−1 K−1) with a thin thickness of 100 μm. Real-time temperature detection demonstrated a subambient cooling of 8.1 °C and an above-ambient cooling of 18.1 °C compared with traditional coating under intense solar irradiation (∼883 W m−2). Such thin PDRC coatings with enhanced thermal dissipation can bring vast opportunities for sustainable applications, and offer an alternative pathway toward achieving effective thermal management.